1. Field of the Invention
The present invention relates to a robot control device for controlling a robot moved according to a force applied to the robot. More specifically, the invention relates to a robot control device of a robot system that moves a robot on the basis of a force applied to the robot that includes a plurality of axes.
2. Description of the Related Art
Direct teaching is known as a robot operation method for moving a robot by applying a force to the robot or a method for teaching a position by moving the robot. In such a case, force is applied in a direction to which the robot is desired to be moved to directly guide the robot, whereby the robot can be moved to a desired position and/or a desired posture on an orthogonal coordinate system.
Japanese Laid-open Patent Publication No. S56-85106 discloses a method for moving a position and a posture of a tip of a robot arm on the basis of a signal generated by a force detector when operating a manual operation unit of the force detector attached to the tip of the robot arm.
Japanese Laid-open Patent Publication No. H6-250728 discloses a direct teaching device. In this device, a force sensor attached to a robot detects an artificially applied force, and with the use of a signal of the force, a position and a posture of the robot are moved while moving a robot arm only in a specific direction on a Cartesian coordinate system.
Japanese Laid-open Patent Publication No. H11-239988 discloses a singular point avoiding method in direct teaching. In this method, when moving the robot in direct teaching, a velocity component that a tip of the robot arm cannot achieve at a singular point is attenuated by a correction formula defined in advance as the tip thereof becomes closer to the singular point. The singular point is a state where the robot is in a singular configuration.
Singular configuration is a posture that results in a state where a position and/or a posture of the tip of the robot arm on an orthogonal coordinate system cannot be uniquely inversely converted to a position of each axis, a posture that results in a state where the position and/or the posture of the tip of the robot arm on the orthogonal coordinate system cannot be moved in a certain direction, and a posture that results in a state where a Jacobian matrix representing a relationship between a velocity of the tip of the robot arm and joint velocity is not a full rank. In the position and/or the posture of the tip thereof near such a singular configuration, it tends to be difficult to change the position and/or the posture thereof on the orthogonal coordinate system, there can be a axis that moves at an excessive velocity, or movement operation of the robot tends to be unstable in positional control. Under such circumstances, an operator may be in danger during direct teaching. To avoid such danger, the conventional techniques relate to a method for decelerating/stopping a robot in direct teaching, a trajectory shifting method for avoiding singular configuration, and the like.
In Japanese Laid-open Patent Publication No. S56-85106, the position and/or the posture of the tip of the robot arm on the orthogonal coordinate system is moved according to the force. Due to this, in the method of Japanese Laid-open Patent Publication No. S56-85106, the tip of the robot arm cannot be moved near singular configuration. In addition, in Japanese Laid-open Patent Publication No. S56-85106, the position of desired each axis cannot be moved during direct teaching.
In Japanese Laid-open Patent Publication No. H6-250728, when moving the robot by direct teaching, the moving direction of the robot is limited to the specific direction to improve operability. The specific direction is a direction associated with the position and/or the posture of the tip of the robot arm on the Cartesian coordinate system. Accordingly, Japanese Laid-open Patent Publication No. H6-250728 does not propose limitation to a axis to be driven and the like, such as switching to control of each axis and driving of only a specific desired axis in direct teaching.
In Japanese Laid-open Patent Publication No. H11-239988, the trajectory is changed by setting the velocity component that cannot be achieved at the singular point to zero so that the tip of the robot arm does not pass through the singular point. As a result, in Japanese Laid-open Patent Publication No. H11-239988, the trajectory can be shifted in a direction different from the direction of the force applied to the robot, whereby the robot can be moved to a position not intended by the operator. Additionally, a certain task requires movement of the robot to a position near a singular configuration. However, even in such a case, in Japanese Laid-open Patent Publication No. H11-239988, the robot cannot be moved to or near the singular configuration.
The present invention has been accomplished in view of such circumstances. It is an object of the invention to provide a robot control device that, when moving a position and/or a posture of a tip of a robot on an orthogonal coordinate system by moving the robot with application of a force to the tip of the robot arm, allows the tip thereof to be moved to a position to which it is difficult or impossible to move the tip thereof. In addition, during the movement of the position and/or the posture of the tip of the robot arm on the orthogonal coordinate system by applying a force to the tip thereof, it is desired that a robot moving mode is switched without using any specific input device or the like and without performing any input task or the like for switching the moving mode. Furthermore, it is desired that the robot is moved stably even in the vicinity of a singular configuration during direct teaching.